Machine switching system for telephone exchanges



Oct. 23, 1928. 1,688,725

(3. F. MCCANN MACHINE SWITCHING SYSTEM FOR TELEPHONE EXCHAEGES Filed Nov. 4, 1926 3 Sheets$heet 1 FIG.

L g 76 U] 2 In venfor Got. 23, 1928. 1,688,725

c. F. MCCANN.

MACHINE SWITCHING SYSTEM FOR TELEPHONE EXCHANGES Filed NOV. 4, 1926 3 Sheets-Sheet 2 In vqnf 'r WWW FM Oct. 23, 1928. 1,688,725

C. F. MCCANN MACHINE SWITCHING SYSTEM FOR TELEPHONE EXCHANGES Filed Nov. 1926 3 Sheets-Sheet 5 Patented Get. 23, 1928.

PATENT OFFICE.

CLYDE F. MCCANN, OF SAN MACHINE SWITCHING SYSTEM Application filed November This invention pertains to a new metnod of machine switching for telephone systems. The object of the invention is to provide a simple, inexpensive, reliable quick acting machine switching system for telephone systems. I

The present svstems in use for machine switching are, as i'ar as is known, all operated upon the step by step method or principle. That is, the calling subscriber, upon raising his hook and dialing a number say 1234, sets certain apparatus or machinery in motion, which hunts first thru the thousands, then the hundreds, then the tens and finally the units until the required number is found, and the connection is made. Upon the establishment or a connection and conversation between the two subscribers, certain switches and multiple banks of contacts are held up and used during the length of the conversation or holding time. The cost of the present machine switching installation therefore, varies not only in proportion to the number of subscribers, and number of calls per maximum busy hour, but also roughly'in proportion to the average holding time of the individual subscribers.

A method of machine switching then which would eliminate the use 01"- any expensive apparatus during the holding time of a subscribers connection would be quite a step in advance of present methods as far as cost at leastis concerned. This I firmly believe the present invention *ill do. Further, com-' paratively little multiple wiring and banking is required in this system,an additional great saving in cost of installation.

Now a brief and general description 01 this invention. First, in this system, the jack of each subscriber is made on the design of a key, working on the principle of combina- 'tions of numbers. In an exchange having numbers of four digits, say numbers 1000 to 9999, there are nine digits in the thousands, ten digits in the hundreds, ten in the tens, and ten in the units, or 39 digits in all. From combinations of these 39 digits, 9000 possible telephone numbers can be made. Substitute now for these 39 digits 39 magnetically operated rods, against which rest lugs of 9000 subscribers jacks, each ack having four lugs corresponding to that particular subscribers number. Now if a calling subscriber can dial a number of four successive digits, store up FRANCISCO, CALIFORNIA.

EEGR- TELEPHONE EXCHANGES.

i. 1923. Serial No. 146,175.

thesame, and then instantly operate tour corresponding magnetically controlled rods, plugging the called subscribers ja 'k and his own to a common line, he will have made a direct telephone connection. This is what is done in the present invention, and therefore a suitable name for the same would be The key system of machine switching for telephone exchanges.

In this system then, briefly, a subscriber removes his receiver from the hook and dials a set of numbers whichare recorded in his individual unit at the exchange or'lice. Upon completion of his dialing and the line being clear, these numbers are switched upon corresponding magnets, which operate attached rods and plug the called subscribers ack and at the same time the callers jack unto a set of battery bus bars, accomplishing a direct con ncction. The battery .bus bars and connected jacks are then auton'iatically raised to an out of the way position, and magnets and all other apparatus restored to normal, so that another connection of any other two subscribers can be quickly made. The two connected subscribers can then communicate with each ther for any length. of time, and at minimum installation cost, for the only apparatus used during the length of a convei .ition or holding time are the two jacks and a pair of battery bus bars. Upon hanging up of the receivers, the jack; drop back to normal.

It will be noted in this system, that each subscriber has attached to his line an inexpensive numbor recording unit. This means that any time spent in dialing a number does not hold up anyone else, or tie up the main switching apparatus, so that the key switching machinery is occupied at all times in constantly plugging in jacks and making connections.

New referring to the drawings Figures 1, 2 and 3 show the outline of the key system of machine switching with suitcient detail equipment for connecting two subscribers. Fig. 1 shows the subscribers local phone and dial unit connected to the individual recording and switch equipment at the switching station. Fig. 2 is a duplicate of. Fig. 1 showing another subscribers equipment. Each subscriber in the system has a similar equipment. Fig. 3 shows the key switching bank common to all the subscribers which has a ack and key for each one. Fi".

3 is drawn in perspective for the sake of clearness. The wiring from Fig. 1 and Fig. 2 can be readily t "aced to Fig.

Let us now trace the circuits and operation in detail, and assume that subscriber A, Fig. 1 desires to make connection with subscriber B, Fig. 2. The subscribefis house phone equipment needs no detailed explanation, being standard for most automatic systems. Subscriber A lifts receiver from hook (2) thereby establishing a direct current loop thru dial 3, transmitter 4, hook switch 2, -inductance 5, via subscribers line 5 and 7 to switching station. the ringer switch unit 8 and are attached re spectively to blades 9 and 10. This ringer switch disconnects the ringer from the circuit and also the recording unit at the proper time, and will be more fully described later.

Normally the blades of the ringer switch are held against contacts 11 and 12 by the tension of spring 13. The blades also make sliding contact with lugs 14 and 15. The circuit then, from subscribers wire 6 goes thru blade 9 of the ringer switch, thru lug 14, wire 16, magnet 17, wire 18, to the plus terminal of battery 19 and finally to ground. Tracing the circuit from subscribers wire 7, it goes thru blade 10, lug 15, wire 20, the primary 21 of transformer 22, wire 23, magnet 24 and to ground. A direct current circuit or loop has been made. One result of this is that magnet 17 is energized and pulls down on iron core 27, causing switch blades 9 and 10 to break contact with lugs 11 and 12 which function in the ringer circuit. The blades are pulled down far enough by magnet 17 however, tomake contact with lugs 25 and 26. The above operation is a preparatory one and has no immediate effects.

Another result of the making of this loop is that magnet 24 is energized and brings relay switch 28 into contact with terminal lug of wire 29, sending a current from battery plus thru wire 29 to magnet 39 and to ground. Now magnet 30 has a core 31 which is attached to lever 32 whose pivot axis is 33. Pivoted at the upper end of lever 32 is an idler roll 34 whose other pivot point is on arm 35 which swings about axis 36. Behind and close to roll 34 is regulating ratchet 37 and recording ratchets 38, 39 and 40. Just be hind these 'atchets is the power friction roll 41. This roll is being driven at a uniform speed by a motor and turns in such a direction as to move the ratchets upward when they press against it.

Now referring again to magnet 30, this having been energized, pulls core 31 outward, thus acting on lever 32 and forcing idler roll 34 inward. This action pinches the ratchets between rolls 34 and power roll 41 so that the ratchets will move upward when released by their pawls. This also is a preparatory action.

The lines 6 and 7 enter One more effect produced by the making of the loop or circuit by the subscriber is to act upon transformer 22. Transformer 22 has a primary 21 and a secondary 42, from which lead wires 43 and 44 to shaded core magnet 45. Magnet 45 operates on pawl 46. Consider what happens when the subscriber raises his hook switch. A direct current is sent thru the primary winding 21 of the transformer 22. The expanding magnetic flux of this current cuts the secondary winding 42 causing a brief flow of current thru lines 43 and 44 and magnet 45. Magnet 45 being energized, draws the lower end of pawl 46 toward it releasing regulating ratchet 3'? which moves upward one-half notch until caught by the tooth on the upper end of pawl 46. Upon secession of the flow of current, magnet 45 loses its flux and the pawl 46 being pulled back by its spring, allows the regulating ratchet to raise one-half notch higher, or a total of one full notch. The lug 4. of regulating ratchet 37 has now come into slid ing contact with stationary lug 48 connected by wire 49 to magnet 50 whose other "criminal is grounded. The making of this contact between the lugs 47 and 48 completes a circuit via wire 20, wire 51, ratchet 37, lug 47, lug 48, wire 49, magnet 50 to ground, thus energizing magnet 50 with direct current. Magnet 50 therefore draws pawl 52 toward its core, which releases the engaged tooth on ratchet 38 and allows it to raise one half notch, in which position it is held by the retaining action of the upper tooth of paw 52 and the continued holding of magnet 50. This one-half notch raise of ratchet 38, however, has not yet brought its lug 53 in con tact with lugs 54.

To summarize briefly the action so far,-

subscriber A lifts receiver 1 from hook switch 2 completing an electrical circuit with battery 19 as source of current supply. This energized magnet 17 of ringer switch 8 accomplishing a preparatory switching movement. Magnet 24 is also energized, causing relay switch 28 to energize magnet 30 which forces roll 34 against ratchets 37, 38, 89 and 40, which in turn press against power roll 41. These four ratchets then tend to raise when released from their pawls. Also the making of this loop circuit acts on transformer 22 and magnet 45 causing ratchet 3'? to raise one notch and make contact with lug 48. This in turn energizes magnet 50, cansing ratchet 38 to raise one-half notch. The above action simply prepares the subscribers individual apparatus at the switching station for receiving the numbers to be dialed by the calling subscriber. The subscriber then is now ready todial a number.

These sketches Figs. 1, 2 and 3 show an equipment for numbers of three digits, that is numbers from 111 to 999.

Let us now assume that subscriber A, Fig.

"eco-nd digit.

1 desires to call a subscriber whose phone number is 222, and that this subscriber to be called is B, Fig. 2. He proceet s to dial the first number #2 on dial 3. The details of the dial are not shown because this is standard cquipn'ient. The dialing he does by placing his linger in dial hole #2 and turns the dial to the stop lug and th eleases The dial then automatically retui to normal, mean while breaking the loop circuit twice, and therefore making it twice. Let us see now the results oroduced in subscriber As equipment at the station.

In the first place the quick break and make of the circuit has not opened the relay switch 28 on account of the shaded core or shorted ring of magnet which holds the magnetic flux thru short interruptions'of the current.

remains in operation dur- Therefore roll ing the dialing ready, to raise the ratchets.

Now consider the effect of dialing the first digit upon regulating ratchet 37 which is operated by magnet 45.

During the break and make operation of the line circuit thru primary winding 21, an alternating current is induced in the secondary circuit which energizes magnet 45 and thus draws over pawl i6, and holds it there on account of the shaded core of magnet 45. This raises the ratchet 37 one half notch though it is still in contact with lug 48. Now, however, when the dial is back to normal, and a steady flow of current is in the line circuit, the current ceases in the secondary circuit, and magnet 15 releases pawl l6 advancing the ratchet 87 another one-halt notch into contact with lug 55, and clear out lug 4&8, thus preparing the circuit for the operation of ratchet 39 on the dialing of the Meanwhile, magnet 50 has acted on pawl 52 to raise recording ratchet 38 two whole notches so that its lug 53 now rests against #2 bar of S t. In other words 4:;2 or the hundreds has been recorded. he banks of bars shown in cross-section in the upper part of Fig. 1 and Fig. 2 are the same in both and common to all the subscribers.

Subscriber A next dials the second digit of the nui'nber The circuit for magnet 57 has been prepared via ratchet 8?, lug 55, and wire 56. Tn dialing, the subscriber breaks and makes the circuit twice on magnet 57, causing pawl 58 to allow the recording ratchet 39 to raise two notches, and bring lug 59 to rest against bar #2 01" the tens bank 60. 'lhereiore digitai2 ot the tens has been recorded. As the current in the subscribers loop becomes steady again, regulating ratchet notches so that lug 6.3 rests against #2 bar of units bank 66. The number 222 has now been recorded.

Subscriber A can do nothing further now to get his party, so that the remaining action at the switching station must automatically connect subscriber A with sub. :riber B. Also subscriber B must be rung, this ringing to be audible to subscriber A. and the'ringer must be'disconnected from the circuit when E lifts his receiver. These automatic operations are accomplished as below.

d When the loop current becomes steadv after the diang ot the last digit of the called number, ratchet 37 ope 'ated by magnet 45 rais s one-hall notch and its lug 47 makes contact with mg 67 sending the loop current via wire 68 to magnet 69. ldagnet 69 thus energized has sutlicient power to pull up switch 70. Now each subscriber has a similar switch. The object of this switch is to put battery voltage viathe recording bars into the proper jack magnets shown in Fig. 3 and thus release two subscribers jack arms and plug the two jacks to common bus bars. Now this is donealmost instantly, but only one connection can be made at one time on one jack bank as of Fi 3. Therefore, it is neces sary to arrang that only one calling subscribers jack magnet switch such as 70 will go in at one time. This is accomplished by the hold back wire Tl which is common to all the subscribers jaclomagnet switches, and is shown common to Fig. 1 and Fig. 2. lVhen-ever any subscribers ack-magnet switch is in. the hold-back wire 71 becomes charged plus from battery 19.

Let us assume for the moment that subscriber Bs switch is in and line 71 charged plus. Then direct current goes from line 7] thru lug 72, thru switch 73 to hold back magnet 7 a and to ground. The hold back magnet 74.- is so wound as to produce a magnetic field tending to i'niniinize the hold of magnet 69. Therefore as long as magnet '74 energized-from wire 71, magnet 69 is pro hibited from drawing up switch 70. As soon hold-back wire 71 is clear of voltage, however, magnet (59, when energized will throw up switch 70.

Coming back to subscriber r s call now. we left off at the point where magnet 69 was energized from wire 68. lVith line 71 cleared, magnet 69 throws switch 70 up. As the switch rises, arm 75 strikes switch 73 and disconnects line 71 from hold-back magnet 74-. The object of this is to keep the subscribers own voltage from energizing magnet 74 and throwing out his switch 70. Next the blades of switch 70 are all thrown in. blade 76 to ratchet 38, blade 77 to ratchet 39 and blade 78 to ratchet 40. Blade 80 puts plus voltage on hold-back wire 71, prohibiting Otl'1l SL1li) scribers switches from being thown in at that instant. Blade 79 puts roltage on wire 81 which goes to subscriber As individual jack magnet shown in F' 3. Ratchets 38, 39 and 10 have now put plus voltage on wires 82, 83 and 8%, which go to the correspond jack magnets of the key controlled plus: bank Fig. 3. to Fi 3.

3 is a perspective view of the key jack-plugging machine whicn plugs together any two subscribers coming into that exchange. It the telephone tiatiic is too great a. mu tiple of this plugging bank can be installed. Fig. 3 shows an outline of the plugging machine, and subscribers l and Bs l-ieys, jack arms and jacks in detail. A row of plugging solenoids 85 plug in the ack of any called subscriber.

The numbers possible to call lie between 111 and 999. There are a. total of twenty-seven plugging solenoids, nine in the hundreds, nine in the tens ant. nine in the units. It number say 179 is called, solenoids #1 hundreds. #7 tens, and #9 of the units are energized and pull to the right their cross bars, allowing the key and jack arm at subscriber 179 to move in the same direction and pin jack 179 into the battery bus bares. In the inrure, only six plugging solenoids are shown, or numbers 1 and 2 each of the hundreds, tons and units. (a) Shows subscriber i'is key jack equipment, and (5) sho' s subscriber Bs equipment.

Let us continue now with subscriber As call #222 to subscriber 13. Lines 82, 83 and 8 1- have been made live with plus battery voltage, thus energizing solenoids 86, 87 and 88 respectively, whose other terminals are grounded. Now each solenoid has a sliding iron core rod, the right end of which is attached to a compression spring bearing; against stationary plate 39, and the left end attached to a horizontal cross bar. Thus solenoid 86 operates bar 90, solenoid 87 bar 91, and solenoid 83 bar 92.

Examining subscriber Bs jack equipment (Z1) we find that this consists of, first a solid T shaped unitmade up of a vertical plate 93, rigidly attached to a horizontal arm or rod 9st. terminating in a head which carries a horizontal ring 93. Rig-idly attached to plate 93 is subscriber Bs key solenoid 97. The core rod. 98 01' this solenoid is attached firmly to key 99 whose three lugs bear against bars 90. 91 and 92 respectively. The key 99 is slidable with relation to plate 93. The pull. of tension spring 100 on core rod 93 normally holds key 99 at rest against pins 101 and 102 which are attached to plate 93. Tension spring 103 attached to arm 94 and plate 89 keeps the lugs of key 99 pressed against bars 90, 91 and 92. Hold loosely in the spring ring 96 of rod head 95 is subscriber Bs jack 10 1-. This jack is equipped with tour clips, the inner two for battery connection, and the outer two for ringer connection. From jack 1051 leads cable a Let us now trace these circuits 105 containing wires 106 and 107 from the battery clips, and wires 10S and 109 from the ringer clips.

l'leturning now to the making of subscriber his call to subscriber B. Plugging solenoids 80, 87, and 38, being energized, pull down bars 90, 91, and away from the lugs of key 99. This allows spring 103 to pull rod 9+1 to the right plugging in the clips of jack 10st into horizontal bus bars 110. The inner clips make contact with the inner battery bus bars, and the outer clips with the outer ringer bus bars.

At the same time that subscriber Bs jack plugs in, subscriber irs jack is being plugged in. In Fig. 1 wire 81 has already been energized by As swii ch 70. 11 i re 81 leads to key solenoid 111 of jack unit (a). Solenoid 111 being energized, pulls its core rod 112 and key 113 to the left against the tension of spring 11 1 and away from pins 115 and 116. This action pulls the lugs of key 113 away from bars 117, 118 and 119, and allows tension spring 120 to pull rod 121 and attached plate 122 to the right, plugging subscriber As jack 123 to the bus bars.

1V0 have now directly connected together the jacks of subscribers A and B via the bus bars 110.

The next objective is to raise the bus bars and attached jacks to an out of the way position so that another pair of subscribers may be plunged to another bus bar set. For this purpose, the bus bar elevator is provided. shown to the right of Fig. 3. This consists of a pair of belts or chains 12 1, and 125 passing around pulleys 126, and 127. A power triction pulley 128 rubs against pulley 129 which is attached to pulley 126 tending at all times to raise the left side of the belts upward. Attached horizontally between belts 12 1 and 125 are bus bar sets similar to 110 and equally spaced all around the outer edge of the belts.

Bing-er 130 is shown wired to brushes which bear on slip rings 131 and suppl Y ringing current via wires 132 and 133 to the outer bus bars 01 110.

Battery supplies direct current to slip rings 135. From one of these slip rings leads wire 137 to an inner bus bar of 110 and in this line is impedance coil 136. From the other slip ring leads impedance coil 13S and wire 139 to switch 140 and clamping magnet 141. The other terminal of magnet 14.1 is connected to the lower inside bus bar of 110. It will be noted that the upper and lower bars of 110 are pivoted, and that the lower bars are at tached to a lever arm 1 12 held lightly in a horizontal position by a tension spring. Lines 1 13 and 1 1-1 lead from inner battery clips of subscriber As jack 123. Lines 1 15 and 1&6 lead from the outer clips.

When jack plugs into the bus bars 110, battery 13% is looped to subscriber A. Starting with battery 13%, this circuit goes thru impedances 136 and 138, wires 137 and 139, magnet 141 and the inside bars 110, inside clips of 123, wires 143 and 144 to subscriber As ringer switch, Fig. 1. Line 143 goes to magnet 147 thru to lug 25 on the switch. Line 144 goes direct to lug 26. Blade 9'is in contact with lug 25, and blade 10 incontact with lug 26, being held there by magnet 17. Therefore, a loop is completed from battery 134 to lines 6 and 7 to subscriber A.

Magnet 147,being in the circuit, is energized and pulls core 27 and switch blades further down on lugs 25 and 26, breaking contact with lugs 14 and 15. This disconnection breaks the loop on lines 18 and 20, de-energizing magnets 24, 30 and 69, so that roll 34 falls away from the ratchets allowing them to drop back by gravity to their neutral position. Also switch drops out, and subscriber As re cording unit is restored to normal.

Referring again to Fig. 3,1nagnet 141 is energized by the loop from battery 134 to subscriber A. It therefore draws down arm 142 thus clamping the middle clip 01 the two jacks 104 and 123 tightly between the upper and lower bus bars of 110. At the same time, magnet 141 draws up switch 140 which makes contact with lug 148 mounted on the same block. Lug 148 makes sliding contact with stationary spring'149 which connects via wire 150to ratchet-wheel magnet 151 whose other terminal goes via wire 152 to the other side of battery 134. Magnet 151 is thus energized, and draws pawl 153 to the right. This allows ratchet wheel 154 to turn clockwise one-half notch until caught by the lower tooth of pawl 153. At this stage the bus bars and belts 124 and have moved upward so that lug 148 has broken connection with spring 149. This breaks the current thru magnet 151 allowing spring 155 to restore the pawl to normal, and the ratchet wheel 154 to turn one.- half notch more in a clockwise direction.

This action brings bars 110 to a clear out of the way position and also brings a lower set of bus bars into the exact position formally occupied by bars 110 on line with the bank of jacks, andready for a new plugging connection.

The throwing out of switch 70 of subscriber A, Fig. 1 has also de-energized plugging solenoids 86, 87 and 88, and key magnet 111 so that jack units a and Z are back to normal except that the jacks themselves 104 and 123 are clamped in bus bars 110 and raised one step or notch higher. The jacks have risen vertically thru the horizontal spring rings of the jack rods. All the main parts of the system are restored to normal now, and subscriber A is directly connected to subscriber Bs line.

Now subscriber B is being rung. The ringer is electrically connected at all times via wires 132 and 133 to the outside bus bars of 110. This puts ringing voltage on the This voltage is impressed on As lines and 146 which are open ended at terminals 11 and 12 on account or the ringer switch being held down by magnet 147. Therefore this ringing voltage does not directly affect As receiver.

Tracing the ringing current in Be circuit, Fig. 2, we tind it goes via lines 108 and 109 to terminals 156 and 157 on Bs ringer switch. The blades 158 and 159 are held by spring 160 against terminals 156 and 157. Therefore, ringing current passes via these blades thru line wires 161 and 162 to subscriber Bs local phone set. Here, the ringing current goes thru dial switch 163, condenser 164, bell 165 and to the other line, thus making a circuit and ringing the bell 165.

WVhile subscriber Bs bell is ringing, subscriber A hears a buzzing in his own receiver to let him know that B is being called. This is accomplished by employing a condenser and resistance. in series, attached on each side of the ringer switch blades as shown by 166 and 167. The ringer voltage from terminal 156 goes thru blade 158, condenser and resistance 166, thru lug 168, magnet 170 to line 106. From terminal 157, the ringer voltage is impressed thru blade 159, condenser and resistance 167, and lug 169 to line 107. Tracing lines 106 and 107 to Fig. 3 these lines come to the center clips 01" Bs jack 104 which are in contact with center bus bars 110. The center bars contact with center clips of As jack 123 thus carrying the ringing voltage to lines 143 and 144.

Tracing these lines to Fig. 1, we find they terminate on lugs 25.and 26. Blades 9 and 10 are held in contact with these lugs so that the ringing current passes thru lines 6 and 7 and thru subscriber As receiver 1, making a buzz and indicating to him that subscriber B is being rung.

Referring to Fig. 2. ing the ringing of his bell, picks up receiver 171, raising hook switch 172. This makes a direct current loop from battery 19 via lines 173 and 174 magnet 175, lugs 176 and 177, blades 158 and 159, wires 161 and 162 thru dial switch 163, transmitter 178, switch 172,-

inductance 179 back to line 161.

Magnet or solenoid 175 thus energized,

pulls down core making blades 158 and 159 contact with lugs 168 and 169 respectively. This contact makes a loop with bat tery 134, Fig. 3 via lines 106 and 107, energizing solenoid 170 which pulls core 180 still further down and disconnects the blades 158 and 159 from lugs 176 and 177 breaking battery 19 loop to subscriber B. The pulling down of which switch blades 158 and 159 has also broken contact with terminals 156 and 157, thus disconnecting subscriber 13' directly and subscriber A indirectly' from the ringer.

The direct connection of subscriber A with subscriber B has now been accomplishe Subscriber B, hear- They can communicate for an indefinite length of time and are not using up expensive apparatus during their holding time. During this holding time other subscribers connections are being made by the jack plugging machine. Meanwhile the bus bars are rising a notch at a time and carrying the jacks with them.

Let us now assume that subscriber B hangs up his receiver. This breaks the loop, and throws up his ringer-switch back to normal. Then subscriber A hangs up. the current in wires 143 and 14 i and deenergizes magnet 141, allowing lever 14-2 to raise, unclamping bus-bars 110, and allow ing A and Bs jacks 123 and 10% to fall out and drop back in to the jack rings, ready for another connection.

Thus we have traced thru one complete call between subscriber A and I3. It is obvious that since Bs equipment is a duplicate of As, the call could be reversed with 13 calling up and making a connection with A. Also it is evident with this key system that a large number of subscribers can easily and quickly make connections with each other.

In Fig. 3 it will be noticed that bus bars 110 as they rise upward on the elevator belts will finally pass over the top of pulley 126 and go down the opposite side and eventually return under pulley 127 to rise up again.

Let us assume that it takes an average during the busy hour, of a period of say one half hour for the bus bars 110 to rise from a position opposite the jacks to the highest vertical position before making the turn over pulley 126. Let us also assume that two subscribers jacks have been connected to this bus bar and the subscribers have been conversing for the one-hali hour period; It is quite obvious that it would not do for the jacks to e arried over the pulley with the bars. Therefore a safety device could readily be provided which would trip out the jacks as they reached the highest vertical position of the bars. This device would limit the subscribers to a onehal;t hour holding time during the maximum busy hour of the day.

A telephone exchange operating with the above method of machine switching can be compared in certain respects to a safe-deposit box system in a bank. In the bank, each customer has an individually numbered sate deposit box and an individual key. Two keys are required to open any box, the customers key and the bank attendants key. The attendantmay be likened to the calling subscriber in a telephone exchange, and a bank customer likened to a called subscriber. The bank attendant inserts his key and the customers key into the lock of the numbered box and opens the box. In this telephone exchange, the calling subscriber raises his receiver hook (inserts his key) dials the num- This breaks ber of the subscriber to be called (inserts the customers key), and accomplishes a tele phone connection or opens up communication (opens the sate deposit box). The keys for opening the bank boxes are flat steel pieces having lugs and depressions cut out of one side and are very similar in appearance and function to the individual jack key pieces of this machine switching system. In its essentials, therefore, this system can well be called the key system of machine switching.

A very important point to be considered in this invention is that in a single exchange office, say of 10,000 lines, there is no multiplying of subscribers lines required, thus saving an enormous amount of wiring and also repair expense due to faulty contacts, etc.

From previous description, it is seen that the subscribers calls are stored up individually and released in turn upon the line connecting machine shown in the drawings. In a single machine, only one pair of subscribers can be connected at one time. It might seem at. first thought, therefore, that in a 10,000 line exchange otiice, one such machine could not take care of the telephone traiiic by making only one connection at a time. However, the eiliciency of this line connecting machine varies directly with its speed of operatic-n. As its members are all electro-magnetically operated, which action is almost instantaneous, there is good reason for assuming that at least an average of two connect-ions per second could readily be made by this machine. There being 3600 seconds in an hour, then 7200 connections per hour could be made, which is more than ample for a 10,000 line ottice.

It would seem quite possible to have a. 20,- 000 or 30,000 line otfice with this system, should it be found necessary. Two switching machines could be used in such an oliice, all the called lines represented in each machine, but one-half the calling lines in one machine, and the other half in the other machine. This ar 'angement is similar to the arrangement of a. multiple switch-board. In a large city where, on account of economy in wiring, it is necessary to have local switching oiiices in the exchange and a trunking system, it will be found that this key system adapts itself readily to trunking.

lVhilc I have shown and described the preferred embodimentof my invent-ion, I wish it to be understood that I do not confine myself to the precise details of the construction herein set forth, by way of illustration, as it is apparent that many changes and variations may be made therein, by those skilled in the art, without departing or exceeding the scope of the appended claims.

I claim:

1. In a machine for connecting the calling and called lines of a telephone system, line jack members keyed to correspond to the line numbers, digit members retaining the keyed line members, connective means opposing the line jack members, means to withdraw the digit members by the calling line, releasing the called line jack upon the connective means, means to release the calling line jack upon the connective means by the calling line, and means to ring the called line.

2. In a switching machine for connecting electrically the calling and called lines oi a numbered line system, a line jack for each line, a bank of jack-holding members each equipped with a key-piece tor-med to corre spond to its line number, a bank of movable digit rods bearing against the key pieces, eachrod representing a digit of the numbers of the system, a movable battery bus bank iior electrically connecting and holding any two linejacks and situated opposing the bank of line-jacks, electroanagnets for operating the digit rods releasing the keyed jack holder and plugging the called line-jack to the battery bus bar set, an individual electro-magnet for releasing the calling keyed jack-holder and plugging the calling line-jack to the battery bus bar set, electromagnetic means to step the jaclcconnected bus bar set and bring the next bus bar setto oppose the line of jacks, means to ring the called line, and means to restore jacks to normal on completion 0t call.

3. In a number recording mechanism or a machine switching system for telephone eX- changes, a set of digit bus bars for each set of digits or" the numbers of the exchange, said bus bars individually electrically connected to corresponding electro-magnets actuating digit rods in the central switching machine, a ratchet contact rod for each set of digits making sliding contact with corresponding set of digit bus bars, a friction power roll for raising ratchets into contact with digit bus bars, an electro-magnet and pawl mechanism for controlling the rise of each ratchet rod, said electro-magnet being actuated by pulsating current from a subscribers number sending device, an electroanagnet in the subscribcrs loop circuit actuating an idle roll which applies friction power roll to ratchet digit rods, a set of control lugs, each connected to a corresponding digit ratchet magnet a control ratchet rod making sliding contact with control lugs connected to the subscribers loop circuit line and raisable by action of power and idler rolls, an electromagnet and pawl for controlling the rise of the control ratchet rod, said electromagnet receiving cur rent from the secondary of a transformer whose primary is in the subscribers loop cir cuit, an additional control lug in the above lug set electrically connected to a magnet for operating a ack magnet switch, a ack magnet switch for placing voltage upon digit ratchet rods and calling subscribers indivi dual jack magnet, and for placing voltage upon a hold-back line to keep other sub scribers jack magnet switches from throwing in.

t. In a telephone system, a subscribers line ringer switch normally connected to open ringer lines and recording mechanism, magnetic means in said switch to disconnect the subscribers line from ringer lines, and connect the subscribers line to open jack lines when the subscribers loop is made, electromagnetic means in said switch to disconnect the subscribers line from the recording mechanism when the jack line circuit is made, and means to restore the switch to normal when the subscribers loop is broken.

In a machine switching system for telephone exchanges; individual means at the switching station tor automatically recording the numbers dialed by the subscriber on a calling line, means to impress said called nmnbers upon a central switching machine, a switching machine for connecting the calland called lines of the exchange, said switching machine comprising line jack members keyed to correspond to the line numbers, digit members retaining the keyed line members, connective means opposing the line jack inen'ibers, means to withdraw the digit members by the calling line, releasing the called line jack upon the connective means, means to release the calling line jack upon the connective means by tl e calling line, and means to ring the called line.

In a machine switching system for telephone or hangcs; individual means at the switchirg station for automatically recording the numbers dialed by the subscriber on a calling line, means to impress said called numbers upon a central switching machine, a switching machine for connecting the calling and called lines oi the exchange, said switching machine comprising-a line jack for each line, a bank oi jack-holding members each equipped with a key-piece termed to correspond to its line number, a bank of movable digit rods bearing against the key pieces, each rod representing a digit of the numbers or the system, a movable battery bus bar bank for electrically connecting and holding any two line-jacks and situated opposing the bank of line-jacks, electro-magnets for operating the digit rods releasing the keyed ack holder and plugging the called line-jack to the battery bus bar set, an individual electro-magnet for releasing the calling keyed jack-holder and plugging the calling line-jack to the battery has bar set, electromagnetic means to step the jaclcconnected bus bar set and bring the next bus bar set to oppose the line of acks, means to ring the called line, and means to restore the jacks to normal on completion of the call.

7. In the number recording mechanism of a telephone system, a set of digitbus bars for each set of digits of the numbers, electrically connected to corresponding digit nieinber magnets in the line connecting machine, a ratchet contact rod for each set of digits making sliding contact with corresponding set of digit bus bars, a power driven friction roll with suitable operating means to step ratchets relative to di git bus bars by calling line, automatic means to apply calling line to operate stepping means of each ratchet consecutively in order of digits called, means to apply voltage to ratchets upon recording of B11111 bers.

CLYDE F. MCCANN. 

